1. Field of the Invention
The present invention relates to systems and methods of water purification, and, more particularly, the control of nutrients, suspended and filamentous algae, pollutants, and toxins in a body of water.
2. Description of Related Art
Many freshwater lakes and ponds, as well as estuaries, are characterized, particularly during the warmer months, by certain contaminants, such as dissolved color, suspended solids, phosphorus, and heavy metals. Another site of contaminated water is the so-called “waste stabilization pond” (WSP), a body of water used to store industrial, municipal, agricultural wastewater or contaminated groundwater. The WSP is believed to be the most prevalent type of wastewater treatment technology in the world.
Chemical coagulants often are used in water treatment to remove contaminants from the water. In lake water treatment, for example, entire lakes or ponds may be treated with coagulants (typically the aluminum compound “alum”). These are added at or above a “critical” concentration, dictated by water chemical characteristics such as water pH and alkalinity, so that a floc forms. Contaminants in the water column are then encapsulated by, or adsorbed to, the floc, which then settles to the bottom of the lake.
It is also known in the art to treat wastewater with conventional “concrete and steel” chemical technologies, using separate chambers for: (1) adding and mixing coagulant; (2) rapid mixing to form flocs; and (3) clarifying to permit settling of flocs, subsequently allowing a clear supernatant to flow out from a port near the top of the vessel.
Alternatively, it is known to inject a coagulant into a water inflow pipe just prior to feeding the water into a lake. This may be accomplished, for example, using a flow proportional injection of coagulant into a stormwater inlet pipe, or by injecting the coagulant into a pipe as it feeds into a wetland. In these cases, the floc accumulates in the lake or wetland over time. In yet another method, prior to entering the lake the floc is fed into a clarification or separation vessel, where the floc is captured and disposed of in a sanitary sewer or is used for land application.
For the above-mentioned “concrete and steel” systems, the goal is to achieve a certain pollutant outflow concentration. For the chemical treatment of stormwater feeding into a lake or wetland, the goal is typically focused on mass (or percentage) removal of contaminants. In all cases, however, there is a clear incentive to minimize chemical dose to minimize cost. In cases in which the floc is captured, another goal is to maximize the settling rate of the floc, which minimizes the “carry-over” of floc from the clarifier, since effective floc settling reduces the required size of the clarifier.